acceleration loss, diagnosis

[lbo]

My 07 Kymco Super 9 has lost some performance, acceleration specifically. It has been getting progressively worse and I think I narrowed it down to a weakening contra (torque) spring.

The engine seems fine, I still have the same top speed but it just requires a lot of distance to get there. It shifts too early, it's fine up to about 25-30 then bogs heavily like the gearing is too tall. It finally comes up to speed and RPM's climb when it gets back in the powerband.

The roller weights are fine, no flat spots. I switched them from the mix of 6.5g/7.0g to lighter 6.0g weights. This helped, tremendously, for a little while at least. Now it's pathetically slow again but top end is still there.

I ordered a new heavier contra spring and waiting to install it. What else could it be? The belt seems fine and not stretched (Dealer looked at it too) so I am not sure if there is something else I am overlooking.

Could this spring be getting weaker and cause this issue? Anything else I am over looking? It has about 5500km on it.

Thanks

[kaintuckdave]

When's the last time you cleaned your air filter?

[lbo]

maybe 2000km's ago or so. I'll check it out but I don't see how it can be ripping close to 10,000 RPM's if it was the filter though.... when it shifts the RPM's drop to ~5700.

Also I just re-packed the silencer on the technigas pipe (didn't fix existing problem), tire pressure is good and the new spark plug has about 300km on it.

[kaintuckdave]

I'm really new to scooting, but I've read a bunch and if your air filter or exhaust are even a bit clogged, it can cause all sorts of trauma to your motor and bring performance down dramatically. Seems like you stated in that 2-stroke best oil thread that you used the good stuff, so I'm thinking air filter. My manual says to clean my air filter every 3000 clicks, but maybe you ran through something that clogged it a bit? That would make a world of difference if so.

Sorry, I'm a noob, but trying to help none the less.

[motomech]

What brand oil?
I would pull the pipe off and take a look into the exhaust port. Often, a performance loss problem on a two-stroke can be traced to carbon building up in the port and starting to close it off.

[lbo]

Thanks for the help. The oil I use is Bel-Ray Si7.

I cleaned the air filter yesturday, wasn't really dirty and it made no noticible difference. I just received my contra spring direct from China yesturday and I will put that in this weekend.

The carbon buildup around the exhaust port makes sense, I bought the performance pipe used. (Technigas Type R). I am leary of taking it off though, one of the studs is a little bent and afraid it will break off. There is no exhaust leak though, certain of that.

I will see what this spring does, adjust the rollers until I get the right weight. If this doesn't help then maybe look at that exhaust. The bike is ready (I am ready) for a 70cc upgrade soon anyway (pipe, cylinder, carb) so if I have some worn rings or other engine related problem it would be a good time to do this.

[lbo]

got my spring in, used the same roller weights. I have a strange rattle in there, and it feels weird. Should I lighten up the rollers with a heavier spring or go lighter? I have read lighter rollers with heavier spring, but it seems logically just the opposite to me.